1. Field of the Invention
The present invention relates to a resin-impregnated substrate.
2. Description of the Related Art
Recently, it is desired to develop an insulating resin substrate excellent in characteristics such as heat resistance, low moisture absorption, dimensional stability and dielectric properties at high frequency, the substrate being used with a conductive layer thereon in electronic and electric equipment fields.
A conventionally known insulating resin substrate is a resin-impregnated substrate which is produced by impregnating glass cross with an epoxy resin (see, Japanese Unexamined Patent Application Publication No. 5-8224).
However, such a resin-impregnated substrate produced by impregnating glass cross with an epoxy resin is insufficient in heat resistance, while the substrate is often used with a lead-free solder which needs a higher temperature in soldering (for example, a temperature of 260° C. or higher). For example, the immersion of the resin-impregnated substrate in a solder bath at a temperature of 260° C. or higher may cause heat deterioration of the epoxy resin, which may result in distortion of the resin-impregnated substrate in some cases. Accordingly, a resin-impregnated substrate having a high heat resistance at such a high temperature under soldering conditions has been demanded.
In addition, the conventional resin-impregnated substrate tends to have a relatively large linear expansion rate. Therefore, when the resin-impregnated substrate is utilized with a conductive layer thereon in the applications of a printed circuit board and a package substrate, the difference in a linear expansion rate between the substrate and the conductive layer is remarkable in some cases. In such cases, warpage of the substrate with the conductive layer may occur when an IC chip is actually mounted thereon. Accordingly, a resin-impregnated substrate having a small linear expansion rate has also been demanded.